Hyaluronic-acid immobilized monodisperse magnetic nanocrystals (HA-DN/MNCs) are synthesized. Dopamine, the analogue of 3,4-dihydroxy-L-phenylalanine responsible for the adhesion properties in proteins excreted by mussels, plays a key role in the surface modification of nanocrystals. HA-DN/MNCs exhibit great stability in aqueous solution, applicable for in vivo targeted-cancer imaging.